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      Impact of MLC properties and IMRT technique in meningioma and head-and-neck treatments

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          Abstract

          Purpose

          The impact of multileaf collimator (MLC) design and IMRT technique on plan quality and delivery improvements for head-and-neck and meningioma patients is compared in a planning study.

          Material and methods

          Ten previously treated patients (5 head-and-neck, 5 meningioma) were re-planned for step-and-shoot IMRT (ssIMRT), sliding window IMRT (dMLC) and VMAT using the MLCi2 without (−) and with (+) interdigitation and the Agility-MLC attached to an Elekta 6MV linac. This results in nine plans per patient. Consistent patient individual optimization parameters are used. Plans are generated using the research tool Hyperion V2.4 (equivalent to Elekta Monaco 3.2) with hard constraints for critical structures and objectives for target structures. For VMAT plans, the improved segment shape optimization is used.

          Critical structures are evaluated based on QUANTEC criteria. PTV coverage is compared by EUD, D mean, homogeneity and conformity. Additionally, MU/plan, treatment times and number of segments are evaluated.

          Results

          As constrained optimization is used, all plans fulfill the hard constraints. Doses to critical structures do not differ more than 1Gy between the nine generated plans for each patient. Only larynx, parotids and eyes differ up to 1.5Gy (D mean or D max) or 7 % (volume-constraint) due to (1) increased scatter, (2) not avoiding structures when using the full range of gantry rotation and (3) improved leaf sequencing with advanced segment shape optimization for VMAT plans. EUD, D mean, homogeneity and conformity are improved using the Agility-MLC. However, PTV coverage is more affected by technique. MU increase with the use of dMLC and VMAT, while the MU are reduced by using the Agility-MLC. Fastest treatments are always achieved using Agility-MLC, especially in combination with VMAT.

          Conclusion

          Fastest treatments with the best PTV coverage are found for VMAT plans with Agility-MLC, achieving the same sparing of healthy tissue compared to the other combinations of ssIMRT, dMLC and VMAT with either MLCi2 −/+ or Agility.

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          Most cited references43

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          A simple scoring ratio to index the conformity of radiosurgical treatment plans. Technical note.

          I Paddick (2000)
          A conformity index is a measure of how well the volume of a radiosurgical dose distribution conforms to the size and shape of a target volume. Because the success of radiosurgery is related to the extremely conformal irradiation of the target, an accurate method for describing this parameter is important. Existing conformity ratios and indices used in radiosurgery are reviewed and criticized. It will be demonstrated that previously proposed measurements of conformity can, under certain conditions, give false perfect scores. A new conformity index is derived that gives an objective score of conformity for a treatment plan and gives no false scores. An analysis of five different treatment plans is made using both the existing scoring methods and the new conformity index.
          Article 0 comments Cited 199 times – based on 0 reviews     Review now
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            Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer.

            Dirk Wolff, Florian Stieler, Grit Welzel … (2009)
            Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques. Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200 degrees rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D(95%) (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered. For MIMiC/IMRT(MLC)/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving > or =70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for > or =50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for > or =30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D(95%) was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min. All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.
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              Is a single arc sufficient in volumetric-modulated arc therapy (VMAT) for complex-shaped target volumes?

              Matthias Guckenberger, Anne Richter, Thomas Krieger … (2009)
              To compare step-and-shoot intensity-modulated radiotherapy (ss-IMRT) with volumetric-modulated arc therapy (VMAT) for complex-shaped target volumes with a simultaneous integrated boost (SIB). This retrospective planning study was based on 20 patients composed of prostate cancer (n=5), postoperative (n=5) or primary (n=5) radiotherapy for pharyngeal cancer and for cancer of the paranasal sinuses (n=5); a SIB with two or three dose levels was planned in all patients. For each patient, one ss-IMRT plan with direct-machine-parameter optimization (DMPO) and VMAT plans with one to three arcs (SmartArc technique) were generated in the Pinnacle planning system. Single arc VMAT improved target coverage and dose homogeneity in radiotherapy for prostate cancer. Two and three VMAT arcs were required to achieve equivalent results compared to ss-IMRT in postoperative and primary radiotherapy for pharyngeal cancer, respectively. In radiotherapy for cancer of the paranasal sinuses, multiarc VMAT resulted in increased spread of low doses to the lenses and decreased target coverage in the region between the orbits. The complexity of the target volume determined whether single arc VMAT was equivalent to ss-IMRT. Multiple arc VMAT improved results compared to single arc VMAT at cost of increased delivery times, increased monitor unites and increased spread of low doses.
              Article 0 comments Cited 60 times – based on 0 reviews     Review now
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                Author and article information

                Contributors
                Steffi Kantz: Steffi.Kantz@med.uni-muenchen.de
                Matthias Söhn: Matthias.Soehn@med.uni-muenchen.de
                Almut Troeller: Almut.Troeller@med.uni-muenchen.de
                Michael Reiner: Michael.Reiner@med.uni-muenchen.de
                Helmut Weingandt: Helmut.Weingandt@med.uni-munenchen.de
                Markus Alber: malb@oncology.au.dk
                Claus Belka: Claus.Belka@med.uni-muenchen.de
                Ute Ganswindt: Ute.Ganswindt@med.uni-muenchen.de
                Journal
                Journal ID (nlm-ta): Radiat Oncol
                Journal ID (iso-abbrev): Radiat Oncol
                Title: Radiation Oncology (London, England)
                Publisher: BioMed Central (London )
                ISSN (Electronic): 1748-717X
                Publication date (Electronic): 2 September 2015
                Publication date PMC-release: 2 September 2015
                Publication date Collection: 2015
                Volume: 10
                Electronic Location Identifier: 184
                Affiliations
                [ ]Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany
                [ ]Department of Radiation Oncology, William Beaumont Health System, Royal Oak, MI USA
                [ ]Department of Clinical Medicine, Department of Oncology, Aarhus University, Aarhus, Denmark
                Article
                Publisher ID: 447
                DOI: 10.1186/s13014-015-0447-z
                PMC ID: 4556413
                PubMed ID: 25567003
                SO-VID: a78cfd85-7b27-46e3-9de3-5e60a33e755b
                Copyright © © Kantz et al. 2015
                License:

                Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                Date received : 23 February 2015
                Date accepted : 25 June 2015
                Categories
                Subject: Research
                Custom metadata
                issue-copyright-statement © The Author(s) 2015

                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: mlc properties,imrt,vmat
                Data availability:
                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: mlc properties, imrt, vmat

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